Ltd., Capetown, South Africa and has been on the market since 1957. 

 It has made possible, for the first time, a means of measuring dis- 

 tances accurately with a small portable unit usable in the field. The 

 tellurometer is an electronic device that uses the pulse type system 

 and consists of two units, the master and the remote. A pulse of radio- 

 frequency energy is transmitted to the remote unit, analyzed, and 

 transmitted back to the master unit. The interval between signals is 

 read in successive steps as millimicroseconds and recorded. The 

 trace appears as a circle on a calibrated graticule which covers the 

 face of a cathode ray tube. The velocity of propagation of the wave 

 is known, and the distance is merely one-half the product of the 

 tellurometer reading and the propagation velocity. Weather conditions 

 affect the velocity and are taken into account, by a slight correction 

 made in the computed distance. Altimeter readings are taken, or 

 vertical angles read, to determine elevation differences since the 

 tellurometer gives the slant distance only. 



This is a line-of- sight device that operates on 3,000 megacycles. 

 On the face of each unit are a cathode ray tube, switches, and meters; 

 the back of each unit has a parabolic antenna. One man can operate 

 each unit, but since all the readings are taken at the master unit, time 

 is saved if one man reads and another records; a man at the remote 

 unit merely switches frequencies. Each unit weighs 38 pounds, and the 

 power pack, storage battery, and tripod account for another 35 pounds. 

 A set-up can be made, several readings taken, and the instrument 

 repacked in about 30 minutes. Readings may be made night or day and 

 in fog or damp, cloudy weather. Rain and snow prevent accurate 

 readings, but this disadvantage is not considered significant. As with 

 the geodimeters, the power source is a troublesome aspect when the 

 batteries have to be carried any great distance. 



Lines that appear to be accurate often prove to be inaccurate because 

 of interference from objects below or along the line. Thus, experience 

 is required to know just how to avoid inaccurate lines. Often, move- 

 ment of either unit a few feet eliminates the trouble. The maximum 

 range is 38 to 40 nautical miles with first-order accuracies obtainable 

 in the longer lines by virtue of measurement of longer time intervals. 

 For short lines of two miles or less, measurements approach second- 

 order accuracy. With two or more remote units, several lines can be 

 measured in a short time. The cost of one set, both master and remote 

 units, is approximately $9,000. 



c. Microdist 



This instrument system is similar to the tellurometer in 



XV- 6 



